1. Technical Field
The present invention relates to an image processing apparatus, an image processing program, an image adjusting apparatus, and an image adjusting program.
2. Related Art
A number of image adjusting techniques are known. In one basic method, color balance correction, chroma emphasis, etc. are performed by analyzing a histogram of pixel signals. To emphasize an outline or edges of a subject in a photograph image, it is common to perform frequency emphasis processing such as unsharp masking. Frequency emphasis processing produces an effect of making an outline or edges of a subject and hence its shape clear. Frequency emphasis processing is performed while adjusting the emphasis band and intensity (gain) using Gaussian function type filtering processing, unsharp masking, or the like.
In band emphasis, the degree of emphasis (reproduction intensity) is adjusted by controlling coefficients. Since the reproduction intensity is adjusted according to an image, the image needs to be analyzes as preprocessing. In band emphasis, in general, high-frequency components (edges) are emphasized. The degrees of variation of edges are calculated from a luminance component of an image and band emphasis is performed using coefficients that are suitable for the calculated degrees, whereby a reproduction image that conforms to the original image is obtained.
Not that the emphasis of high-frequency components such as edges provides a satisfactory result for every image. The adjustment target band varies depending on a scene represented by an image; for example, it may be a low-frequency band and a medium frequency band or a high-frequency band that is close to a medium frequency band. And the reproduction intensity varies depending on the adjustment target band. It is therefore necessary to select a band that is suitable for an image and to adjust the reproduction intensity in the selected band.